Optical head device, optical recording device, and optical recording method

ABSTRACT

An object of the present invention is to acquire optimum recording characteristics of an optical recoding medium having multiple data layers, with respect to each of the multiple data layers without increasing learning time required for learning a relation between aberration amount and optimum recording compensation with respect to each of the multiple data layers. The present invention includes a wavefront converter which is driven in such a manner as to reduce the aberration amount detected by an aberration detector. An output controller holds learned data as to the relation between the driving amount of the wavefront converter and the output of a light source, and controls the output of the light source based on the driving amount of the wavefront converter and the learned data.

TECHNICAL FIELD

The present invention relates to an optical head device, an opticalrecording device, and an optical recording method for recording and/orerasing information on an optical medium or an opto-magnetic medium suchas an optical disk or an optical card, and particularly to an opticalhead device, an optical recording device, and an optical recordingmethod suitable for recording and/or erasing data on an opticalrecording medium having multiple data layers (e.g., a multi-layeredoptical disk or a multi-layered optical card).

BACKGROUND ART

There has been developed use of a light source of a shorter wavelength,and a focusing lens having a larger numerical aperture (hereinafter,simply called as “NA”) in order to increase the recording capacity of anoptical disk. The wavelength of the light source and NA of the focusinglens used in DVDs are generally 650 nm and 0.6, respectively. There hasbeen proposed an optical system for optical disks of future generationin which the wavelength of the light source is 405 nm, and NA of thefocusing lens is 0.85. Technology is being developed regardingmulti-layered optical disks constructed such that a number of datalayers are laminated one over another at a certain interval in thethickness of the optical disk in an attempt to further increase therecording capacity of the optical disk.

Increase of NA of a focusing lens may resultantly increase sphericalaberration relative to a variation (unevenness) in thickness of asubstrate of an optical disk. The thickness of the substrate hereinmeans a thickness of the substrate from the light receiving plane of theoptical disk to the recording layer thereof. Since spherical aberrationdue to substrate thickness variation is proportional to the fourth powerof NA, a spherical aberration of 10 mλ (=0.01 λ) is generated as thesubstrate thickness is varied by 1 μm in the optical system in which thewavelength of the light source is 405 nm, and NA of the focusing lens is0.85. A coma aberration, which is generated by tilting of the opticaldisk relative to the optical axis of the focusing lens, is increased, asNA is increased, even with the same tilting amount. A sphericalaberration or a coma aberration may degrade data recordingcharacteristics. Accordingly, it is a common practice to detect anaberration of a light spot focused by the focusing lens, and control theoutput of the light source so as to compensate for the recordingcharacteristics. This conventional art is disclosed, for example, inJapanese Unexamined Patent Publication No. 2001-160233 (patent document1).

There has been known, as a method for detecting spherical aberration, atechnology of dividing received light reflected from an optical diskinto several areas on a cross-sectional flat plane of the light beam,and detecting a focus error signal with respect to each of the areas tocalculate aberration. This technology is disclosed, for example, inJapanese Unexamined Patent Publication No. 2000-182254 (patent document2).

Regarding coma aberration, there has been known a technology ofdetecting tilting of an optical disk with use of a tilt sensor providedin an optical head device, and calculating aberration based on thedetection result. Regarding a multi-layered optical disk provided withmultiple data layers, there is proposed an arrangement in which anaberration compensator is provided to compensate for sphericalaberration with respect to each of the data layers, in light of the factthat the substrate thicknesses differ from each other with respect tothe data layers. Examples of the aberration compensator are: the one inwhich a transparent plate member is provided between the focusing lensand the optical disk for compensating spherical aberration; the one inwhich wedge-like transparent blocks are assembled together to set theoptical path length from the focusing lens to the respective data layersidentical; and the one in which a diverging lens and a converging lensare arranged at respective appropriate positions between the focusinglens and the collimator lens for making laser beams from the lightsource into parallel light beams, and the distance between the divergingand converging lenses is rendered variable by a voice coil motor forcompensating spherical aberration. These aberration compensators are,for example, disclosed in Japanese Patent No. 2502884 (patent document3).

The working distance corresponding to the distance between the focusinglens and the optical disk is from 0.2 to 0.6 mm when NA of the lens tobe used is 0.85. Therefore, it is difficult to arrange a plate member orwedge-like blocks between the focusing lens and the optical lens,considering vertical displacement of the optical disk arising fromrotation of the optical disk, or vibrations exerted from the outside. Inview of this, there is generally provided an aberration compensatorbetween the collimator lens and the focusing lens. In the arrangement,recording characteristics of the multi-layered optical disk arecorrected by compensating the spherical aberration with respect to eachof the data layers before controlling the output of the light sourcebased on the detected aberration amounts.

Aberration correcting means such as an aberration compensator forcompensating the aberration with respect to each of the data layers isrequired in the optical head device for use in recording/reproducingdata on an optical disk having multiple data layers. The aberrationcorrecting means is adapted to reduce the aberration, which is supposedto be generated in applying the focusing lens designed such that theaberration is set to 0 with respect to a specific substrate thickness,to a data layer having a substrate thickness different from the specificsubstrate thickness. The aberration correcting means is driven tominimize the aberration amount detected by the aberration detectingmeans provided in the optical head device. Let us assume an arrangementin which a third-order spherical aberration is to be detected, and theaberration correcting means is so designed as to reduce such athird-order spherical aberration. Such an arrangement makes it possibleto set the third-order spherical aberration to 0 with respect to anydata layer by controlling the aberration correcting means to make laserlight incident on the focusing lens into converging light or diverginglight. Despite such a merit, however, the above arrangement fails to setthe total aberration including aberration of the fifth and higher ordersto 0, with the total aberrations with respect to the data layers beingdifferent from each other. In this way, if the above proposedarrangement regarding aberration detection and aberration reduction isapplied to the multi-layered optical disk having multiple data layers, adetected aberration amount and an actual aberration amount are differentfrom each other. A similar drawback should be considered, as the orderof aberration to be detected is raised from the fifth order to theseventh order or the like, as long as undetectable aberration of ahigher order remains. Therefore, the recording characteristicscompensating method in which the output of the light source iscontrolled based on the detected aberration amount, as having beenemployed in the conventional art, fails to carry out optimum recordingcharacteristics compensation, because output control is not executedwhen the detected aberration amount of a low order is 0 although thereactually remain aberrations of a higher order which are different fromeach other with respect to the data layers. Furthermore, according tothe conventional method, information is required as to the layer numberof the target data layer, in addition to information relating to thedetected aberration amount, and it is required to optimize the recordingpower based on such information. Thus, the conventional arrangement notonly necessitates a program for learning a relation between theaberration amount and the optimum recording power with respect to eachof the data layers, and for storing the learning results, but also makesthe program complicated.

More specifically, if the aberration detecting means for detecting thethird-order spherical aberration is used, and aberration correction isimplemented with use of the aberration compensator based on thethird-order spherical aberration amount detected by the aberrationdetecting means in recording/reproducing data on the first data layerand the second data layer whose distances from the optical disk surface(light receiving plane) are different from each other, it is more likelythat a relation between the detected third-order spherical aberrationamount and the optimum recording compensation amount, namely, correctionresidual with respect to the data layers may be varied from each other.

FIG. 11 shows a relation between substrate thickness variation, andthird-order spherical aberration, and total aberrations, based on thesubstrate thickness of the optical disk as a parameter. The totalaberration herein means aberration including third-order sphericalaberration and aberration of the order higher than the third order. InFIG. 11, the aberration is compensated by the aberration compensatorsuch that the third-order spherical aberration is 0 when the substratethickness variation is 0. The substrate thickness variation in FIG. 11is a variation relative to the respective initial thicknesses of thefirst and second data layers (e.g., 100 μm for the first data layer, and110 μm for the second data layer), i.e., a relative value in thickness.Furthermore, the variation is not an average of thickness variation, asrepresented by “rms” or a like unit, but is an instantaneous value. Asis obvious from FIG. 11, aberration amounts of the order higher than thethird order are different from each other between the first data layerand the second data layer, although the third-order spherical aberrationamounts are identical to each other between the first and second datalayers. Even if the aberration detecting means acquires aberrationamounts of the higher orders such as the fifth order, seventh order orthe like, there still remains a difference in aberration component ofthe order higher than a highest order detectable by the aberrationdetecting means between the first and second data layers. Consequently,since the relation between the aberration amount detected by theaberration detecting means, and the optimum recording compensationamount is different from each other with respect to the data layers, itis required to provide a program corresponding to learning means (notshown) that learns a relation between the aberration amount and theoptimum recording compensation amount with respect to each of the datalayers in advance for recording compensation, and stores the learningresults therein. In this way, the technical field of the presentinvention has encountered problems such as increase of learning hoursand increase of the quantity of the program, with increase in the numberof data layers.

DISCLOSURE OF THE INVENTION

In view of the above problems, an object of the present invention is toprovide an optical head device, an optical recording device, and anoptical recording method that enable acquisition of optimum recordingcharacteristics of an optical recording medium having multiple datalayers, with respect to each of the multiple data layers withoutincreasing learning hours required for learning a relation between anaberration amount and an optimum recording compensation amount withrespect to each of the multiple data layers.

The optical head device according to the present invention isconstructed such that output controlling means controls the output of alight source based on a driving amount of wavefront converting means andinformation relating to a relation between the driving amount and theoutput of the light source.

These and other objects, features, aspects, and advantages of thepresent invention will become more apparent upon reading of thefollowing detailed description and accompanying drawing.

BRIEF DESCRIPTION ON OF THE DRAWINGS

FIG. 1 is an illustration showing an arrangement of an optical headdevice in accordance with a first embodiment of the present invention.

FIG. 2 is a graph showing a relation between a driving amount to be sentfrom aberration detecting means to driving means, and an optimum outputof a light source in correspondence thereto in the optical head devicein accordance with the first embodiment of the present invention.

FIG. 3 is a graph showing a relation between a substrate thickness of anoptical recording medium, and the driving amount to be inputted to thedriving means in correspondence thereto in the optical head device inaccordance with the first embodiment of the present invention.

FIG. 4 is a schematic plan view of an optical recording medium 9.

FIG. 5 is a partially enlarged plan view of the optical recording medium9.

FIG. 6 is a flowchart showing a procedure of learning operation.

FIG. 7 is a graph showing a relation between a driving amount acquiredby the learning, and an optimum recording power.

FIG. 8 is an illustration showing an altered arrangement of the opticalhead device in accordance with the first embodiment of the presentinvention.

FIG. 9 is an illustration showing an arrangement of an optical headdevice in accordance with a second embodiment of the present invention.

FIG. 10 is an illustration showing an arrangement of a multi-layeredoptical recording device in accordance with a third embodiment of thepresent invention.

FIG. 11 is a graph showing a relation between a substrate thicknessvariation, and a third-order spherical aberration and total aberrations,based on a substrate thickness of an optical disk as a parameter.

BEST MODE FOR CARRYING OUT THE INVENTION

In the following, preferred embodiments of the present invention aredescribed referring to the drawings.

First Embodiment

FIG. 1 is an illustration showing an arrangement of an optical headdevice in accordance with a first embodiment of the present invention.The optical head device 101 includes a light source 1, a collimator lens2, a beam splitter 3, wavefront converting means 4, a focusing lens 8, adetection optical system 10, a light detector 11, aberration detectingmeans 12, and output controlling means 13. The light source 1 ispreferably a semiconductor laser which emits laser light of wavelength405 nm. The collimator lens 2 is adapted to make the laser light emittedfrom the light source 1 to parallel beams. The beam splitter 3 isadapted to split the optical path of light. The wavefront convertingmeans 4 has a converging lens 5, a diverging lens 6, and driving means7. The driving means 7 is adapted to drive the diverging lens 6. Thedriving means 7 is preferably a voice coil motor.

An optical recording medium 9 from which or in which data is to be reador written with use of the optical head device 101 has multiple datalayers 9 a, 9 b, 9 c. In this embodiment, described is an example wherethe optical recording medium 9 consists of three layers. It is needlessto say that the number of data layers of the optical recording medium 9to be used by the inventive optical head device is not limited to three.The detection optical system 10 is adapted to focus the reflected lightfrom the optical recording medium 9. The aberration detecting means 12is adapted to, for example, detect third-order spherical aberrationbased on a signal detected by the light detector 11, send a drivingamount for driving the driving means 7 to the driving means 7 to reduce(e.g., minimize) the detected third-order spherical aberration, and alsosend the driving amount to output controlling means 13, which will bedescribed later. The output controlling means 13 is adapted to controlthe output of the light source 1 depending on the driving amount, whichis the output from the aberration detecting means 12.

The output controlling means 13 has learning means 51. A relationbetween the driving amount to be sent from the aberration detectingmeans 12 to the driving means 7, and an optimum recording power incorrespondence thereto has been acquired in advance by the learningmeans 51, as initial learning. Specifically, the learning means 51learns how high the intensity of laser light to be incident on thefocusing lens 8 is to be adjusted, depending on a variation in substratethickness regarding each of the data layers 9 a, 9 b, 9 c of the opticalrecording medium 9, corresponding to a distance between the lightreceiving plane of the optical recording medium 9 and each of the datalayers 9 a, 9 b, 9 c. Information acquired through the learningconsidering the substrate thickness variation is regarded as informationrelating to the optimum recording power relative to the totalaberration, considering third-order spherical aberration and sphericalaberration other than the third-order spherical aberration. The learningmeans 51 causes, for example, a learned data memory 52 equipped in theoutput controlling means 13 to store the information acquired throughthe learning.

The output controlling means 13 is adapted to vary a light emittingduration or peak level of pulse emission, based on the learned datawhich is the information learned or acquired by the learning means 51,and the driving amount outputted from the aberration detecting means 12,for controlling the recording power of the light source 1. The learningmeans 51 may acquire the learned data when the optical recording medium9 having the multiple data layers 9 a, 9 b, 9 c is loaded in the opticalhead device 101.

The output controlling means 13, or the output controlling means 13 andthe aberration detecting means 12 may be constituted by a computer whichis operated in accordance with a program stored in a memory such as aRead Only Memory (ROM). The program is suppliable through a recordingmedium such as an ROM or a CD-ROM, or through a transmission medium suchas a network.

FIG. 2 is an illustration showing a relation between the driving amountto be sent from the aberration detecting means 12 to the driving means7, and the optimum recording power of the light source 1 incorrespondence thereto. The driving amount to be sent to the drivingmeans 7 corresponds to a driving amount based on which the optical headdevice 101 is operated to reduce (e.g., minimize) the aberrationdetected by the aberration detecting means 12. As shown in FIG. 2, therelation between the output of the light source 1 and the driving amountto be sent to the driving means 7 is one to one.

A relation between the driving amount and the optimum recording powerwill be represented by a horizontally straight line as shown by thecurve C1, if the actual aberration does not contain spherical aberrationof the order higher than the order of aberration to be detected by theaberration detecting means 12 (e.g., third order, hereinafter, the orderof aberration to be detected by the aberration detecting means 12 isreferred to as “detected order”), and the wavefront converting means 7can be properly operated by setting the driving amount appropriately,with the result that the spherical aberration of the detected order cannot only be reduced, but also be constantly set to 0. In other words, ifthe above conditions can be satisfied, the optimum recording power maybe set constant without depending on the driving amount. Actualaberration, however, contains aberration of the order higher than thedetected order. Therefore, the optimum recoding power will be asdepicted by the curve C, which is dependent on the driving amount,primarily resulting from aberration of the order higher than thedetected order.

When aberration is generated, effective recording power on a centralregion of a spot of focus light formed on the data layer 9 a or thelike, which effectively contributes to data reading/writing is lowered,as the spot of focus light is enlarged. The lowering of the recordingpower on the effective region can be compensated by raising the outputof laser light to be emitted from the light source 1. This means thatthe more the actual aberration is, the higher the optimum recordingpower is.

The driving amount to be sent from the aberration detecting means 12 tothe driving means 7 varies depending on the substrate thickness of theoptical recording medium 9. FIG. 3 is a graph showing a relation betweenthe substrate thickness of the optical recording medium 9, and thedriving amount to be sent to the driving means 7 in correspondencethereto. The substrate thickness differs depending on which layer datais to be read from or written to by the optical head device 101, namely,on which data layer 9 a, 9 b, or 9 c, the spot of focus light is to beirradiated. In view of this, as the data layer for data reading/writingis changed, the focusing lens 8 is moved forward or backward along theoptical axis of the lens in such a manner as to follow the change of thedata layer by focus control, which will be described later. Aberration,however, is not eliminated even by such a focus control. As exemplifiedin FIG. 3, even if the spherical aberration of the detected order withrespect to the substrate thickness corresponding to the data layer 9 bis 0 at the driving amount of 0, a certain driving amount is required todrive the wavefront converting means 7 if the target data layer ischanged, because spherical aberration of the detected order is generatedas the target data layer is changed, and driving of the wavefrontconverting means 7 is required to compensate for such sphericalaberration. The wavefront converting means 7 is driven in such adirection as to cause diverging light to be incident on the focusinglens 8, as the target data layer is shifted in such a direction as toincrease the substrate thickness, whereas the wavefront converting means7 is driven in such a direction as to cause converging light to beincident on the focusing lens 8, as the target data layer is shifted insuch a direction as to decrease the substrate thickness.

There exists a one-to-one relation between the substrate thickness andthe driving amount, as exemplified in FIG. 3, irrespective of a fact asto whether the relation results from a difference in data layer or avariation in substrate thickness. Likewise, as exemplified in FIG. 2,there exists a one-to-one relation between the optimum recording powerand the driving amount. The relation between the substrate thickness andthe driving amount exemplified in FIG. 3 reflects a relation between thesubstrate thickness and spherical aberration of the detected order whenthe driving amount is 0. This means that information relating to thetarget data layer, substrate thickness variation, and sphericalaberration of the detected order are integrally correlated to thedriving amount, and accordingly, the relation between the driving amountand the optimum recording power has one-to-one correspondence. Thisanalysis leads to a conclusion that the recording power of laser lightcan be set to an optimal value merely depending on the driving amount.

As exemplified in FIG. 3, in the case where the spot of focus light isto be incident on the data layer 9 c, and there exists a substratethickness variation Δt relative to the original substrate thickness t(e.g., average), the aberration detecting means 12 is driven in such amanner as to vary the driving amount from the driving amount Dcorresponding to the substrate thickness t by a driving amount ΔD alongthe curve in FIG. 3. Then, the output controlling means 13 shifts theoptimum recording power from the power P corresponding to the drivingamount D by ΔP corresponding to the varied driving amount ΔD along thecurve C shown in FIG. 2, which illustrates a relation between thedriving amount and the optimum recording power.

The relation between the optimum recording power and the driving amountto minimize the spherical aberration of the detected order, namely, theconfiguration of the curve C as exemplified in FIG. 2, depends on astructural difference such as the substrate thickness of each opticalrecording medium 9, the number of data layers constituting each opticalrecording medium 9, or characteristics variation of the optical headdevice 101 itself or a like factor. In view of this, it is morepractical to acquire the relation between the optimum recording powerand the driving amount by way of the aforementioned learning. Theprocedure on the learning will be described later in detail.

As shown in FIG. 3, the driving amount of the driving means 7 forcorrecting the spherical aberration generated on the optical recordingmedium 9 differs depending on which data layer of the optical recordingmedium 9 the spot of focus light is to be incident. Accordingly, knowingthe driving amount of the driving means 7 makes it possible to grasp onwhich data layer the target focus light spot is located. Allowing theoutput controlling means 13 to receive the driving amount which is sentto the driving means 7 means that the output controlling means 13receives information regarding which data layer 9 a, 9 b, or 9 c of theoptical recording medium 9 the spot of focus light is located, as wellas information relating to the total aberration, which is the sum ofthird-order spherical aberration, and aberration resulting from avariation in substrate thickness of the target data layer.

The optical head device 101 in accordance with the first embodiment ofthe present invention is constructed such that the output of the lightsource 1 is controlled by correlating the driving amount to be sent fromthe aberration detecting means 12 to the driving means 7, to therelation between the driving amount and the optimum recording power ofthe light source 1 that has been acquired as learned data in the outputcontrolling means 13.

Referring back to FIG. 1, the operation of the optical head device 101is described along with the optical path and signal path. The lightemitted from the light source 1 is rendered to parallel beams by thecollimator lens 2, and has its optical path oriented toward the focusinglens 8 by the beam splitter 3. The wavefront converting means 4 turnsthe incoming parallel beams to outgoing parallel beams of a beam sizedifferent from that of the incoming parallel beams when a signalindicative of a correction amount (namely, driving amount) outputtedfrom the aberration detecting means 12 is 0.

The light transmitted through the wavefront converting means 4 isfocused on the data layer 9 a, 9 b, or 9 c of the optical recordingmedium 9 by the focusing lens 8. The focusing lens 8 is so designed asto set the third-order spherical aberration to 0 when the light isfocused on the data layer 9 b at the driving amount of 0 (in this case,the spherical aberration of a higher order is minimized), with theresult that third-order spherical aberrations are generated with respectto the data layer 9 c having a substrate thickness larger than that ofthe data layer 9 b, and the data layer 9 a having a substrate thicknesssmaller than that of the data layer 9 b. The light reflected from theoptical recording medium 9 is impinged on the light detector 11 via thefocusing lens 8, the wavefront converting means 4 and the beam splitter3, and through the detection optical system 10. The light detector 11 isadapted to generate servo signals necessary for driving the focusinglens 8 with use of a focus error signal detection such as a well-knownspot size detection method or three-beam method, and with use of atracking error detecting method.

The aberration detecting means 12 detects spherical aberration,according to the known technique as having been employed in theconventional art, with use of the signals outputted from the lightdetector 11, and moves the diverging lens 6 in such a direction as toreduce (e.g., minimize) the spherical aberration. The driving amountoutputted from the aberration detecting means 12 is sent to the outputcontrolling means 13, as well as to the wavefront converting means 4(driving means 7), so that the output controlling means 13 controls theoutput of the light source 1 based on the output sent from theaberration detecting means 12 (in this example, the driving amount thathas been inputted to the driving means 7).

As described above, the output controlling means 13 acquires therelation between the driving amount to be sent from the aberrationdetecting means 12 to the driving means 7, and the optimum recordingpower through the learning operation of the learning means 51. FIG. 4 isa schematic plan view of the optical recording medium 9. The opticalrecoding medium 9 has a test recording region 32, in addition to a datarecording region 31 for recording user data therein. The test recordingregion 32 is used to record specific data as test data for determiningthe quality of the recorded signals so as to implement a learningoperation for acquiring an optimum recording condition. As shown in FIG.5, the test data are recorded with different outputs in plural zones32(1) through 32(K) of the test recording region 32.

FIG. 6 is a flowchart showing a procedure of the learning operation tobe implemented by the learning means 51. When the learning process ofthe learning means 51 is initiated, the learning means 51 designates thefirst layer (e.g., data layer 9 a) as the target data layer for writingtest data therein (Step S1). Next, the learning means 51 controls theaberration detecting means 12 to set the driving amount suitable for thedesignated data layer (Step S2). Thereby, the driving means 7 drives thewavefront converting means 4 in such a direction as to compensate forthe spherical aberration of the detected order. Subsequently, thelearning means 51 sets the output P of the light source 1 to the initialvalue P0 (Step S3). Then, the learning means 51 allows test data to bewritten in e.g., the zone 32(1) of the test recording region 32 (StepS4). Next, the learning means 51 judges whether the output P is a finaloutput (Step S5). If it is judged that the output P is not the finaloutput (NO in Step S5), the learning means 51 controls the light source1 to raise the output P (Step S6), and implements the processes fromSteps S3 through S5 again. That is, the learning means 51 executeswriting of test data while raising the output P from the initial valueP0 to the final value stepwise. Thus, the learning means 51 successivelyrecords the test data in, e.g., the zones 32(1) through 32(K) each timethe output P is raised.

When the writing of test data is completed (YES in Step S5), thelearning means 51 causes the light detector 11 to read out the test datasuccessively from, e.g., the zones 32(1) through 32(K) (Step S7). Next,the learning means 51 measures jitter of each of the readout test data(varied amount of the reproduced data position relative to the referenceclock) (Step S8). Then, the learning means 51 determines the output Pcorresponding to the optimum jitter (Step S9), and causes the learneddata memory 52 to store the determined output P as the optimum recordingpower, in correlation with the driving amount (Step S10). Next, thelearning means 51 judges whether the data layer is the final layer (StepS11). If it is judged that the target data layer is not the final layer(NO in Step S11), the learning means 51 designates a next layer as thetarget data layer (Step S12), and implements the process of Step S2 andthereafter. If it is judged that the data layer is the final layer (YESin Step S11), the learning means 51 terminates the learning operation.

Thus, the optimum recording powers in correspondence to the respectivedriving amounts are acquired as learned data, and the learned data isstored in the learned data memory 52. In the case where the opticalrecording medium 9 has three layers, i.e., the data layers 9 a, 9 b, 9c, three sets of combinations relating to the relation between thedriving amount and the optimum recording power are obtained, asrepresented by three data points Q1, Q2, Q3, as shown in FIG. 7, forexample. In the learning, a variable component of the driving amountresulting from the substrate thickness variation, namely, the alternatecurrent component of the driving amount (also, called as “high frequencycomponent”) of the driving amount is significantly small, because thezones 32(1) through 32(K) substantially cover one spiral track on theoptical recording medium 9. As a result, as illustrated by the datapoints Q1, Q2, Q3 in FIG. 7, merely an invariable component of thedriving amount, which is the direct current component of the drivingamount corresponding to the difference in data layer, is acquired by thelearning. Thus, the learning means 51 acquires a relation between theoptimum recording power and the driving amount, which is exemplarilydepicted by the curve in FIG. 7, by implementing data interpolation withuse of polynomial expression or spline function based on the data pointsQ1, Q2, Q3. The obtained relation is stored in the learned data memory52 as learned data, and is used in output control by the outputcontrolling means 13.

Since the output controlling means 13 outputs the recording powerdepending on the learned data acquired through the learning, one-to-onerelation is established regarding the total aberration and the optimumrecording power with respect to each of the data layers. This makes itpossible to adjust the degree of convergence or divergence of laserlight incident on the focusing lens 8 with respect to each of the datalayers 9 a, 9 b, 9 c of the optical recording medium 9. This arrangementeliminates determination as to which data layer, 9 a, 9 b, or 9 c of theoptical recording medium 9 the spot of focus light is located, becausethe input to the output controlling means 13 (driving amount to be sentto the driving means 7) includes the information relating to which datalayer 9 a, 9 b, or 9 c of the optical recording medium 9 the spot offocus light is located, as well as the information relating to thespherical aberration.

In this way, acquiring the relation between the driving amount and theoptimum recording power in advance by the initial learning enables tooptimize the recording power with use of the simple program and toexpedite startup of the optical head device without the need ofindependently acquiring information relating to the data layer for datarecording, and without learning with respect to each of the data layerswhich has been required in the conventional art.

The above arrangement is advantageous in simplifying the relationbetween the substrate thickness deviation and recording compensationamount as compared with the conventional art where the recording poweris controlled based on the aberration amount, because, in the abovearrangement, recording compensation is implemented, as long as thedriving amount is not 0 even if the detected aberration amount is 0.

Alternatively, the output control may be executed based on the productof the direct current component and the high frequency component of thedriving amount for the following reason. When the driving amount isseparated into the direct current component (corresponding to thedriving amount D in FIG. 3), and the high frequency component(corresponding to the varied driving amount ΔD in FIG. 3) through afilter, as mentioned above, the direct current component corresponds toeach of the data layers, and the high frequency component corresponds tothe substrate thickness variation (corresponding to the substratethickness variation Δt in FIG. 3), arising from rotation of the opticalrecording medium. As exemplified in FIG. 7, gradients G1, G2, G3 of thecurve at the respective data points Q1, Q2, Q3 are proportional to thedriving amount, or at least increased along with increase of the drivingamount. In view of this, it is possible to obtain a high frequencycomponent of the optimum recording power with high precision bymultiplying the direct current component of the driving amount by thehigh frequency component of the driving amount. As far as the curveexemplified in FIG. 7 is a curve of the second order (parabola), thegradients G1, G2, G3 are proportional to the driving amount. If thegradients G1 through G3 are proportional to the driving amount, the highfrequency component (corresponding to ΔP in FIG. 2) of the optimumrecording power is proportional to the product of the direct currentcomponent D of the driving amount and the high frequency component ΔD ofthe driving amount. Thus, the high frequency component of the optimumrecording power is acquired with high precision.

Further, since the varied amount of the high frequency component isgenerally significantly small, the amplitude of the high frequencycomponent can be enlarged by calculating the product of the highfrequency component and the direct current component. This arrangementnot only accomplishes control of light amount with high precision butalso makes it possible to obtain information relating to the location ofthe target data layer for data recording/reproduction by calculating amaximum amplitude of the varied amount with respect to the product ofthe direct current component and the alternate current component in viewof the fact that the magnitude of the direct current component differsdepending on which data layer the spot of focus light is located.

Alternatively, separating the driving amount into a high frequencycomponent of a significantly small value, and a direct current componentof a significantly large value enables utilization of circuitconfigurations suitable for the respective components. Furtheralternatively, it may be possible to calculate the product of the highfrequency component and the direct current component by applying aweighting factor either to the high frequency component or the directcurrent component, in place of calculating the product while setting theratio of the high frequency component to the direct current component to1:1.

The optical head device 101 feeds back, to the output controlling means13, the driving amount which is outputted from the aberration detectingmeans 12 to the wavefront converting means 4 (more specifically, thedriving means 7). Alternatively, there is proposed an optical headdevice 101A, as exemplified in FIG. 8. The altered arrangement isconstructed such that driving amount detecting means 55 detects thedriving amount of the diverging lens 6, and the driving amount is fedback to the output controlling means 13. It is possible to employvarious well-known conventional movement detectors, as the drivingamount detecting means 55.

Second Embodiment

FIG. 9 is an illustration showing an arrangement of an optical headdevice in accordance with a second embodiment of the present invention.Referring to FIG. 9, elements identical to or equivalent to those inFIG. 1 are denoted by the same reference numerals, and descriptionthereof will be omitted herein. Wavefront converting means 14 shown inFIG. 9 is constructed such that a liquid crystal device 61 is providedbetween electrodes 62 a and 62 b. As is well known, the phase of linearpolarized light can be changed by applying a voltage to the liquidcrystal device. Accordingly, spherical aberration can be corrected byproviding well-known coaxially aligned annular electrodes as theelectrodes 62 a, 62 b, and by changing the drive voltage to be appliedto each of the annular electrodes. Likewise, as is well known in theart, a coma aberration can be corrected by dividing each of the annularelectrodes radially into plural zones. Since the optical head device 102in accordance with the second embodiment of the present inventionemploys the wavefront converting means 14 provided with the liquidcrystal device 61 as mentioned above, the optical head device 102enables lowering of the power consumption, as well as correction of comaaberration.

Third Embodiment

An optical recording device using the inventive optical head device isdescribed as a third embodiment of the present invention referring toFIG. 10. As shown in FIG. 10, the optical recording device 103 includesan optical head device 15, rotation driving means 17, a circuitsubstrate 18, and a power source 19. The optical head device 15 is theoptical head device 101 or the optical head device 101A as the firstembodiment, or an optical head device 102 as the second embodiment. Therotation driving means 17 has a motor for drivingly rotating an opticaldisk 16 as an example of the optical recording medium while supportingthe optical disk 16. The optical disk 16 has multiple data layers.

The optical head device 15 sends, to the circuit substrate 18, a signalindicative of a position thereof relative to the optical disk 16. Thecircuit substrate 18 computes the signal, and outputs a signal forminutely moving the optical head device 15 or a focusing lens 8 in theoptical head device 15. The optical head device 15 or the focusing lens8 in the optical head device 15 implements focus servo control andtracking servo control with respect to the optical disk 16, and readsout data from, writes data in, or erases data from the optical disk 16with use of the circuit substrate 18. The circuit substrate 18 has anelectric circuit for controlling a focus servo driving mechanism (notshown) and a tracking servo driving mechanism (not shown), and for datareading, writing, or erasing. The power source 19 may be a connector tobe connected with an external power source. The power source 19 suppliespower to the circuit substrate 18, the driving mechanisms of the opticalhead device 15, the motor 17, and to a focusing lens driving device. Asan altered form, a power source or a connection terminal to be connectedwith the external power source may be individually provided with respectto each of the driving circuits.

The optical storing device constructed with use of the inventive opticalhead device is advantageous in simplifying the learning regardingrecording compensation with respect to each of data layers, and insimplifying the program for recording compensation, which makes itpossible to expedite startup of the optical storing device.

BRIEF DESCRIPTION OF THE EMBODIMENTS

The following is a brief description on the embodiments of the presentinvention.

An optical head device comprises: a light source; focusing means whichfocuses light from the light source onto a desired data layer of anoptical recording medium having multiple data layers; wavefrontconverting means provided between the light source and the focusingmeans; aberration detecting means which detects an aberration amount ofa spot of the focus light on the desired data layer; and outputcontrolling means which controls output of the light source, wherein thewavefront converting means is driven in such a manner as to reduce theaberration amount detected by the aberration detecting means, and theoutput controlling means holds learned data as to a relation between adriving amount to be inputted to the wavefront converting means, and theoutput of the light source, and controls the output of the light sourcebased on the driving amount to be inputted to the wavefront convertingmeans and the learned data, the driving amount being changed dependingon the aberration of the focus light spot.

The above optical head device not only enables to simplify recordingcompensation with respect to the multiple data layers but also enablesto learn the relation between the driving amount of the wavefrontconverting means and the output of the light source, in place oflearning a relation between the aberration amount and the optimumrecording compensation amount with respect to each of the data layers,as in the conventional art, by controlling the output of the lightsource with use of the output signal to be inputted to the wavefrontconverting means. This arrangement enables to shorten the requiredlearning time and lessen the quantity of the program for the learning,thereby contributing to expedited startup of the optical head device.

Preferably, the optical head device further comprises driving amountdetecting means which detects the driving amount to be inputted to thewavefront converting means, wherein the output controlling meanscontrols the output of the light source based on the driving amountdetected by the driving amount detecting means.

The above arrangement makes it possible to controllably optimize thepower of the light source while correcting the spherical aberrationdepending on each of the data layers of the optical recording medium.

It is desirable that the output controlling means controls the output ofthe light source based on the product of a direct current component andan alternate current component of the driving amount to be inputted tothe wavefront converting means.

The above arrangement enables to increase the amplitude of the highfrequency component of the driving amount. This arrangement not onlymakes it possible to control the light amount with high precision, butalso makes it possible to acquire the information relating to thelocation of the target data layer for data recording/reproduction bychecking the maximum amplitude of the varied amount of the product ofthe direct current component and the alternate current component of thedriving amount. Thus, the output controlling means enables to controlthe power of the light source to the optimum light amount depending oneach of the data layers of the optical recording medium.

Preferably, the wavefront converting means is a liquid crystal device.

The above arrangement enables to controllably optimize the power of thelight source while correcting the spherical aberration depending on eachof the data layers of the optical recording medium.

Preferably, the wavefront converting means includes a plurality oflenses, and lens driving means which drives one of the plurality oflenses to change a distance between the one lens and the other one ofthe plurality of lenses, and the lens driving means is driven in such amanner as to reduce the aberration amount detected by the aberrationdetecting means.

The above arrangement enables to controllably optimize the power of thelight source while correcting the spherical aberration depending on eachof the data layers of the optical recording medium.

Preferably, the output controlling means controls the output of thelight source based on the driving amount and the learned data so as tocompensate for a spherical aberration of the order higher than a highestorder of aberration compensatable by the wavefront converting means.

According to another aspect of the present invention, an opticalrecording device comprises: the aforementioned optical head device, androtation driving means which rotates the optical recording medium.

The optical recording device not only enables to simplify recordingcompensation with respect to the multiple data layers, but also enablesto learn the relation between the driving amount of the wavefrontconverting means and the output of the light source, in place oflearning the relation between the aberration amount and the optimumrecording compensation amount with respect to each of the data layers,as in the conventional art. This arrangement enables to shorten therequired learning time and lessen the quantity of the program for thelearning, thereby contributing to expedited startup of the opticalrecording device.

Further, provided is an optical recording method for recordinginformation on an optical recording medium having multiple data layerswith use of a focus light spot emitted from a light source. The methodcomprises the steps of learning in advance a relation between a drivingamount by which wavefront converting means is to be operated so as toreduce an aberration of the focus light spot, and an output of the lightsource; detecting the aberration of the focus light spot; driving thewavefront converting means so as to reduce the aberration; andcontrolling the output of the light source based on the driving amountof the wavefront converting means.

The optical recording method not only enables to simplify recordingcompensation with respect to the multiple data layers, but also enablesto learn the relation between the driving amount of the wavefrontconverting means and the output of the light source, in place oflearning the relation between the aberration amount and the optimumrecording compensation amount with respect to each of the data layers,as in the conventional art. This arrangement enables to shorten therequired learning time and lessen the quantity of the program for thelearning, thereby contributing to expedited startup of the opticalrecording device.

Although the present invention has been described in detail, theaforementioned description is merely an example in every aspect of thepresent invention, and the present invention is not limited thereto. Itis to be construed that unillustrated numerous modifications andalterations will be embraced in the present invention, unless otherwisesuch modifications and alterations depart from the scope of the presentinvention.

EXPLOITATION IN INDUSTRY

The optical head device, the optical recording device, and the opticalrecording method of the present invention are industrially usefulbecause they enable to acquire the optimum recording characteristics ofan optical recording medium having multiple data layers, with respect toeach of the data layers without increasing learning time required forlearning a relation between aberration amount and optimum recordingcompensation with respect to the multiple data layers.

1. An optical head device for use with an optical recording mediumhaving multiple data layers, said optical head device comprising: alight source operable to output light; focusing means for focusing lightoutputted from the light source onto a desired data layer of the opticalrecording medium having multiple data layers; a wavefront converterprovided between the light source and the focusing means; driving meansfor driving the wavefront converter; aberration detecting means fordetecting an aberration amount of a spot of the light focused on thedesired data layer and sending a driving amount to the driving means fordriving the wavefront converter to reduce the detected aberrationamount; the driving means performing the driving of the wavefrontconverter according to the driving amount sent by the aberrationdetecting means in such a manner as to reduce the aberration amountdetected by the aberration detecting means; and output controlling meansfor storing learned data indicating correlation between driving amountsof the wavefront converter and outputs of light of the light source, andcontrolling the light source so as to set the output of light outputtedby the light source to an output of light indicated in the learned dataas correlating to the driving amount sent by the aberration detectingmeans.
 2. The optical head device according to claim 1, wherein theoutput controlling means controls the light source so as to control theoutput of light output by the light source based on the product of adirect current component and an alternate current component of thedriving amount to be inputted to the wavefront converter.
 3. The opticalhead device according to claim 1, wherein the wavefront converter is aliquid crystal device.
 4. The optical head device according to claim 1,wherein the wavefront converter includes a plurality of lenses, and thedriving means comprises lens driving means for driving one of theplurality of lenses to change a distance between the one lens and theother one of the plurality of lenses in such a manner as to reduce theaberration amount detected by the aberration detecting means.
 5. Theoptical head device according to claim 1, wherein the output controllingmeans controls the light source so as to control the output of lightoutputted by the light source based on the driving amount and thelearned data so as to compensate for a spherical aberration of the orderhigher than a highest order of aberration compensatable by the wavefrontconverter.
 6. An optical recording device comprising: the optical headdevice of claim 1; and rotation driving means for rotating the opticalrecording medium.
 7. An optical recording method for recordinginformation on an optical recording medium having multiple data layerswith use of a focus light spot emitted from a light source, the methodcomprising: storing in advance learned data indicating correlationbetween outputs of light of the light source and driving amounts bywhich a wavefront converter is to be operated to reduce an aberration;detecting the aberration amount of the focus light spot; sending adriving amount to the wavefront converter for driving the wavefrontconverter to reduce the detected aberration amount; driving thewavefront converter according to the sent driving amount so as to reducethe aberration; and setting the output of light outputted by the lightsource to an output of light indicated in the learned data ascorrelating to the driving amount sent in said sending.
 8. An opticalhead device for use with an optical recording medium having multipledata layers, said optical head comprising: a light source operable tooutput light; a focusing system operable to focus light outputted fromthe light source onto a desired data layer of the optical recordingmedium having multiple data layers; a wavefront converter providedbetween the light source and the focusing system; a wavefront converterdriver; an aberration detector operable to detect an aberration amountof a spot of the light focused on the desired data layer and to send adriving amount to the wavefront converter driver for driving thewavefront converter to reduce the detected aberration amount; thewavefront converter driver being operable to drive the wavefrontconverter according to the driving amount sent by the aberrationdetector in such a manner as to reduce the aberration amount detected bythe aberration detector; and an output controller operable to storelearned data indicating correlation between driving amounts of thewavefront converter and outputs of light of the light source, and tocontrol the light source so as to set the output of light outputted bythe light source to an output of light indicated in the learned data ascorrelating to the driving amount sent by the aberration detector. 9.The optical head device according to claim 8, further comprising adriving amount detector operable to detect the driving amount to beinputted to the wavefront converter, wherein the output controller isoperable to control the light source so as to control the output oflight outputted by the light source based on the driving amount detectedby the driving amount detector.
 10. The optical head device according toclaim 8, wherein the output controller is operable to control the lightsource so as to control the output of light outputted by the lightsource based on the product of a direct current component and analternate current component of the driving amount to be inputted to thewavefront converter.
 11. The optical head device according to claim 8,wherein the wavefront converter is a liquid crystal device.
 12. Theoptical head device according to claim 8, wherein the wavefrontconverter includes a plurality of lenses, and the wavefront converterdriver includes a lens driver operable to drive one of the plurality oflenses to change a distance between the one lens and another one of theplurality of lenses in such a manner as to reduce the aberration amountdetected by the aberration detector.
 13. The optical head deviceaccording to claim 8, wherein the output controller is operable tocontrol the light source so as to control the output of light outputtedby the light source based on the driving amount and the learned data soas to compensate for a spherical aberration of the order higher than ahighest order of aberration compensatable by the wavefront converter.14. An optical recording device comprising: the optical head device ofclaim 8; and a rotation driver operable to rotate the optical recordingmedium.
 15. The optical head device according to claim 1, wherein theoutput controlling means comprises a computer.
 16. The optical headdevice according to claim 1, wherein the aberration detecting meanscomprises a computer.
 17. The optical head device according to claim 8,wherein the wavefront converter driver comprises a voice coil motor. 18.The optical head device according to claim 8, wherein the outputcontroller comprises a computer.
 19. The optical head device accordingto claim 8, wherein the aberration detector comprises a computer.
 20. Anoptical head device for use with an optical recording medium havingmultiple data layers, said optical head device comprising: a lightsource operable to output light; focusing means for focusing lightoutputted from the light source onto a desired data layer of the opticalrecording medium having multiple data layers; a wavefront converterprovided between the light source and the focusing means; driving meansfor driving the wavefront converter; aberration detecting means fordetecting an aberration amount of a spot of the light focused on thedesired data layer and sending a driving amount to the driving means fordriving the wavefront converter to reduce the detected aberrationamount; the driving means performing the driving of the wavefrontconverter according to the driving amount sent by the aberrationdetecting means in such a manner as to reduce the aberration amountdetected by the aberration detecting means; driving amount detectingmeans for detecting an amount of the driving of the wavefront converterperformed by the driving means; and output controlling means for storinglearned data indicating correlation between amounts of driving of thewavefront converter and outputs of light of the light source, andcontrolling the light source so as to set the output of light outputtedby the light source to an output of light indicated in the learned dataas correlating to the amount of driving detected by the driving amountdetecting means.
 21. An optical head device for use with an opticalrecording medium having multiple data layers, said optical headcomprising: a light source operable to output light; a focusing systemoperable to focus light outputted from the light source onto a desireddata layer of the optical recording medium having multiple data layers;a wavefront converter provided between the light source and the focusingsystem; a wavefront converter driver; an aberration detector operable todetect an aberration amount of a spot of the light focused on thedesired data layer and to send a driving amount to the wavefrontconverter driver for driving the wavefront converter to reduce thedetected aberration amount; the wavefront converter driver beingoperable to drive the wavefront converter according to the drivingamount sent by the aberration detector in such a manner as to reduce theaberration amount detected by the aberration detector; a driving amountdetector operable to detect an amount of the driving of the wavefrontconverter performed by the wavefront converter driver; and an outputcontroller operable to store learned data indicating correlation betweendriving amounts of the wavefront converter and outputs of light of thelight source, and to control the light source so as to set the output oflight outputted by the light source to an output of light indicated inthe learned data as correlating to the amount of driving detected by thedriving amount detector.